Kaplan General Chemistry Subject Test 1

[Meas]

Kaplan General Chemistry Subject Test 1:

I’ve been working on subject tests from Kaplan and here are some questions that I have since I only have the answer & no explanation. Please help me out as these are the common questions that I always get wrong! Thank you soooo much!

5) Given: H2O (g) -> H2O (l) H=-44kJ/mol
C(s) + O2(g) -> CO2 (g) H=-394
H2(g) + 1/2O2(g) -> H2O(l) H=-286
C2H5OH(l) + 3O2 -> 2CO2(g) + 3H2O(l) H=-1367
2C(s) + 2H2(g) + H2O(l) -> C2H5OH(l) H =+7

Q: What is delta H of formation of H2O(g)?

A: -242kJ/mole

--I used the following & calculated the answer as 190kJ/mole which is not present in the given answer choices:

2(-394) + 3(delta H of formation of H2O) – 7 = -1367

19) A complex of general formation AB6^3- is known to have octahedral geometry. What is the hybridization of the central atom of this ion?

A: sp^3d^2

--When figuring out hybridization, do we simply count the # of valence electrons around the central atom?

Thanks in advance!

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[toothdoc0121]

for number 5

5) Given: H2O (g) -> H2O (l) H=-44kJ/mol
C(s) + O2(g) -> CO2 (g) H=-394
H2(g) + 1/2O2(g) -> H2O(l) H=-286
C2H5OH(l) + 3O2 -> 2CO2(g) + 3H2O(l) H=-1367
2C(s) + 2H2(g) + H2O(l) -> C2H5OH(l) H =+7

use only
H2O (g) -> H2O (l) H=-44kJ/mol
H2(g) + 1/2O2(g) -> H2O(l) H=-286

reverse the first equation to cancel out the H20(l) so its 44 kj/mol and then simply add which would give u -242 kj/mol


for number 19
ocahedral means 6 bonds with no lone pairs so just count the number of bonds and you end up w sp^3 d^2

hope this helps

 

[Meas]

Thank you so much for your help!